advice needed on growing outdoor variety of cucumber inside a polytunnel

This is my first year growing cucumbers and I never researched it properly as it was only until I was ready to plant my cucumber plants in the tunnel that I realised there were both outdoor and indoor varieties and the cucumber seeds I bought were the outdoor type  Marketmore is the variety

Regardless though I planted them in the tunnel close to the doors so they might get the best of both worlds.
When I looked up about growing cucumbers I see that the growing tip is pinched out after 7 leaves have developed and then the plant is allowed to trail over the ground. Where the indoor ones are allowed to grow upwards,
I don't have a lot of room where I have planted them to allow them to trail over the ground so could I grow them upwards even though they are technically an outdoor variety

The method of growing (i.e. upwards or trailing) is not the issue. Outdoor ones need pollinating, indoor ones go bitter if the do.

There should not be an issue as you are only growing one type. You could run into problems if growing both together as the outdoor ones could cross pollinate the indoor ones, which tend to be all female F1 hybrids, so that they don't get pollinated.

As  long as the insects can get to them and you're not trying to grow indoor ones as well, you should be OK.

some people grow cucs up mesh rather than along the ground, i grow around stings. i pinch out the growth tip of the side shoots after one or possibly two cucs, otherwise it gets an absolute mess.

i have also found that if you (well me anyway) sow early to get a quicker crop they seem to exhaust themselves and die off pretty quick. i do half mine early to get the first crop and the rest when the tunnel is hot enough to germinate in. these last ones will last all summer.